Method for production of envolute gear tooth flanks

ABSTRACT

A method and apparatus are disclosed in which only one working point or machining point on a machining tool, which machining contact with a workpiece such as a gear blank during a machining operation. The position of this single working or machining point can be selectively chosen within a machining region of the grinding wheel or disk and can be prescribed to lie in a zone of fixed or variable radius of the grinding wheel or disk. This is achieved through at least one feed motion, in general a feed motion of the grinding wheel or disc, effected in addition to feed motions known per se in machining processes performed essentially according to the indexing generating method. This means that the machining contact point between the grinding wheel or disk and the gear blank does not wander on the grinding wheel or disk in correspondence with the generating feed motions but can be confined to a predeterminate region. It is nevertheless possible to displace this working or machining point in an orderly and programmed manner, i.e. under control, to optimally exploit the machining tool. In accordance with the method, the machining point can be guided along different types of machining lines, for example along lines which at least approximate tooth flank generatrices or along lines which at least approximate tooth traces or flank lines and which may be helical.

BACKGROUND OF THE INVENTION

The present invention broadly relates to a method and apparatus forfabricating involute gear tooth flanks.

Generally speaking, the invention relates to a method for fabricatinginvolute gear tooth flanks without or with geometric corrections bymeans of at least one machining tool and in which method machining, feedand traversing motions between the machining tool and a workpiece orgear blank are performed.

The invention is also concerned with a machine tool or machiningapparatus for performing the method and comprising a machine frame witha generating carriage translatably seated on this machine frame. Themachine tool or machining apparatus further comprises a workpiece orgear blank carrier or support and clamping means for holding a workpieceor gear blank and a multiple-carriage or carriage-and-slide arrangementfor performing the machining, traversing and feed motions. Drive meansas well as control means for carrying out, i.e. controlling andpowering, these movements are also provided.

In a known method of fabricating involute gear tooth flanks, conical ordished grinding wheels are used which each respectively process a rightand a left gear tooth flank. For this purpose, the two grinding wheelsare fixed at an angle in relation to each other such that working ormachining planes of the grinding wheels define the surfaces of ahypothetical generating rack on which the gear to be ground is generatedor rolled. The inclination of the grinding wheels to a normal to thegenerating roll plane or pitch plane is generally the same as thepressure angle α of the gear teeth. The relative motion between themachining tool or grinding wheel and the workpiece or gear blank forgenerating the involute form, the so-called generating roll motion, isderived from the pitch circle. FIG. 6 hereof shows the generatingprocess of a gear wheel on a hypothetical rack in transverse section andin a number of phases. The points A, P, C, T and E delimit segments ofthe line of action which correspond to regions of the tooth flank. Theaddendum flank or flank region is formed on the tooth flank during thegrinding process when the section AC of the line of action is traversed.When the section CT of the line of action is traversed, then an initialor outer dedendum flank or flank region of the tooth flank involute iscorrespondingly formed.

The point T on the line of action is reached when the corner point K ofthe basic tooth rack profile lies on the line of centers OC connectingthe workpiece or gear blank center O with the pitch point C on the lineof action. The section TE of the line of action corresponds to twosegments on the tooth flank which are formed simultaneously (cf. FIG.11): a further or inner dedendum flank portion of the tooth flankinvolute and a trochoidal or undercut dedendum or root fillet radius.The point E is the lowest or innermost point of the involute and at thesame time the initial point of the dedendum or root fillet trochoid orundercut. The curves or semicircles shown in dotted lines in FIG. 11indicate which points of the inner dedendum flank portion of the toothinvolute and of the dedendum fillet or undercut are simultaneouslygenerated.

FIG. 16 shows the working or machining points Pi', Pi" on a dished orflat grinding wheel or disk which is in contact with the tooth flank ofthe workpiece or gear blank. During the grinding process, these workingor machining points wander, depending upon the generating roll positioni, along the machining or grinding surface of the disk and the edges ofthe grinding wheel and each such working or machining point lies on ageneratrix of the tooth flank surface.

During the generating process, a working or machining point of a conicalor beveled grinding wheel will wander along a meridian over a working ormachining width of the grinding disk corresponding to the entire toothflank. Machines or apparatus for such a process are, for example,described in the Swiss Pat. No. 592,604 granted Oct. 31, 1972, and theGerman Pat. No. 2,050,946, granted May 13, 1976. It is a disadvantage ofthis process that topological or geometric flank corrections can only becarried out to a relatively limited extent since due to the forces whicharise between the workpiece or gear blank and the machining tool andother system conditions relative to the size of the gear tooth ingeneral, a larger area of the grinding wheel or disk is involved in themachining process producing the involute form. The working or machiningregions especially can only be very coarsely localized and can beinfluenced only by altering system features which are very difficult orimpossible to carry out, such as grinding wheel size or shape.

SUMMARY OF THE INVENTION

Therefore, with the foregoing in mind, it is a primary object of thepresent invention to provide a new and improved method and apparatus forfabricating involute gear tooth flanks which do not exhibit theaforementioned drawbacks and shortcomings found in the prior art.

Another and more specific object of the present invention is to assurethat the working or machining regions of the grinding wheels can, on theone hand, be kept small and that working or machining points of grindingwheel surfaces can, on the other hand, be predetermined in location forachieving more accurate tooth flank forms and more accurate and specifictopographical or geometric corrections.

A further object of the invention is to provide machine tools ormachining apparatus for performing the inventive method.

Now in order to implement these and still further objects of theinvention, which will become more readily apparent as the descriptionproceeds, the method of the present invention for fabricating involutegear tooth flanks is manifested by the features that working ormachining contact between the workpiece or gear blank and the machiningtool or grinding wheel is confined to a selectable working or machiningpoint or to within the immediate vicinity thereof. The feed motion isperformed such that the working or machining point is guided essentiallyalong a selectably predeterminate working or machining line which liesat least approximately on the tooth flank surface for generating ageneratrix envelope.

The apparatus of the present invention for fabricating involute geartooth flanks is manifested by the features that it comprises guidingmeans and control means for controlling and guiding a selectable work ormachining point on the machining tool along a selectably predeterminateworking or machining line essentially extending along the tooth flanksurface. For this purpose, the guiding means are connected with positiondetermination means which transmit positioning signals to the controlmeans for controlling the driving means.

An advantageous step of the inventive method consists in that thevariably selectable working or machining point of the tool or grindingwheel, or at least a region in the immediate vicinity of this machiningpoint, is confined during the machining operation by a supplementaryfeed motion of the tool to a working or machining region of themachining tool which is prescribable or predeterminate independently ofthe generating process.

A further advantageous step of the method consists in that theselectable working or machining point of the machining tool, or at leasta region in the immediately vicinity of the machining point, is confinedduring the machining operation conjointly by a supplementary feed motionof the machining tool and a supplementary feed motion of the workpieceor gear blank toward the machining tool to a working or machining regionof the machining tool which is prescribable or predeterminateindependently of the generating process.

The supplementary feed motion of the machining tool can be performedalong a symmetry plane or surface of a tooth space.

The supplementary feed motion of the workpiece or gear blank towards themachining tool can also be performed as a translatory motion, a rotarymotion or a pure generating feed motion.

According to a further advantageous method step, the selectable workingor machining point of the machining tool, or at least of a region in theimmediate vicinity of the machining point, is continuously andprescribably or predeterminately displaced within the working ormachining region during the machining operation by means of a work ormachining point feed motion conforming to the wear of the machiningtool.

The supplementary feed motions can be coupled with conventional or basicfeed motions performed along the working or machining line forgenerating involute gear tooth flanks according to their generatrixenvelopes.

For this purpose, the prescribable or predeterminate, i.e. selectablypredeterminate, working or machining line may comprise segments which atleast approximate generatrices of the tooth flank surface.

The prescribable or predeterminate, i.e. selectably predeterminate,working or machining line can also be composed of segments in which afirst branch at least approximate a generatrix and a second branch atleast approximates a profile line.

Furthermore, it is also possible to couple the supplementary feedmotions with the conventional or basic feed motions along the working ormachining line for producing involute gear tooth flanks according totheir flank generatrix or tooth trace envelopes.

The prescribable or predeterminate working or machining line can becomposed or segments which at least approximate tooth traces or flanklines of the tooth flank surfaces.

Alternatively, the prescribable or predeterminate working line can becomposed of sections or segments in which a first branch is at least onetooth trace or flank line and a second branch or segment at leastapproximates a profile line.

The supplementary feed motion can be performed tangentially to the toothflank or tangentially to a tooth flank meridian.

A further possibility is that the control of the working or machiningpoint relative to the machining tool or grinding wheel surface can beperformed in dependence of wear measurements of this machining toolsurface.

The control of the motion of the work or machining point for achieving abetter exploitation of the machining tool can also be performed independence of wear measurements and empirical values.

Furthermore, it is advantageous if the motion of the work or machiningpoint is continuously or discontinuously superimposed on thesupplementary feed motion.

In this inventive method, traversing motion for generating uncorrectedtooth flanks can be performed in at least one stage, i.e. in one or morestages.

In the generation of topographically or geometrically corrected toothflanks, the traversing motion on the selectably prescribable working ormachining line can be performed in at least one stage. The traversingmotions of possible further stages corresponding to the correctionvalues for each correction point are performed continuously.

The traversing motions can be performed either by the machining tool orby the workpiece or gear blank and, here again, can be purelytranslatory, purely rotary or a combination of both types of motion.

All motions can be controlled by prescribable or predeterminate data orfunctions of data.

However, it is also possible for all motions, except generating feedmotions known per se, to be controlled by prescribable or predeterminatedata or functions of data.

The supplementary feed motion can also be controlled such that, givenvariable and continuously measured values for the generating path of theworkpiece or gear blank center and for the longitudinal feed of themachining tool or grinding wheel relative to a reference point on thehypothetical reference or basic generating rack tooth flank tangentsurface, the distance of the common working or machining point of themachining tool and of the workpiece or gear blank from a referencepoint, for example from the reference point on the reference or basicgenerating rack tooth flank, at least approximately satisfies theequation:

    ys=h·tan γ+(w·sin αt)/cos γ(1)

The means of guidance of the apparatus for carrying out the method cancomprise at least one slide or carriage providing at least onesupplementary degree of adjustment freedom for the motion of themachining tool or tools.

One slide or carriage can also be provided for each machining tool as aguide means so that the machining tool or tools and their associatedworking or machining point are, in addition to all other motions, alsodisplaceable tangentially to the tooth flank surface.

At least one slide or carriage can be provided as a guide means for afeed motion of the machining tool radial to the workpiece or gear blank.It is also possible to provide a slide or carriage for a feed motiontangential to the gear tooth flank.

Furthermore, the control means for controlling the generating feedmotion can be mechanical means of control known per se, while thecontrol means for controlling all other motions, or for that matter allof the motions, can be electronic circuitry means.

It is especially advantageous for the electronic circuitry means tocomprise a master computer or control processor connected to:

a master control interface for signal input and output;

a grinding wheel control means for regulatory controlling at least onegrinding wheel drive means;

a carriage control means for conjointly controlling appropriate drivemeans for standard pressure angle, tooth helix angle and motion of theintermediate slide or carriage to adjust or regulate the pressure angleadjustment;

an adjustment means for adjusting the tooth helix angle and at least oneintermediate slide or carriage;

supplementary feed control means for controlling at least one drivemeans for at least one supplementary feed motion of each machining tool,for example either by means of a slide or carriage or as a resultant ofa number of conjoint feed motions;

a traversing control means for controlling at least one drive means fornormal traversing motions, topographical or geometrical correctiontraversing motions or both; and

a measuring control means for operating a grinding wheel measuring ormonitoring means and also connected to the control means for controllingthe other motions.

The machining tool can comprise a dished grinding wheel or disk of atype known per se, a conical or beveled grinding wheel or disk of a typeknown per se or a dished grinding wheel or disk whose working ormachining surface is a frustum of a cone with an included or cone angleslightly less than 180°.

An important advantage of the inventive method consists in that, even incomparison to the topographical or geometric correction relationships,larger and therefore more stable grinding wheels or disks or also othertypes of machining tools, for instance milling cutters, can be employed.This also entails other economical and technological advantages. Inparticular, in comparison to known methods, only a relatively small zoneof the grinding wheel or disk need be sensed for wear monitoring andmeasurement. The controllable displacement of the active grinding zoneentails, among other things, the additional advantage of an improvedself-sharpening effect and therefore a considerably better exploitationof the grinding wheel or disk. The working or fillet radius cantherefore also be controllably and considerably improved and machined.

The adjustability of the grinding wheel or disk is also improved due tothe improved controllability of the active machining zone or region ofthe grinding wheel or disk as a result of its working or machiningregion being reduced in size and of the controllable displacement of theworking or machining point. The topographical or geometric correctionscan also be carried out considerably more accurately and with betterdistribution by means of such a controllable and practically definableworking or machining point. The end or final values as well as controlvalues for geometric correction are more easily mastered and betterrealisable, or are only thus possible. Difficult running properties ofgears can be mastered and corrected considerably more specifically andtherefore better than hitherto. The accuracy of fabrication is betterand therefore better suited to specific conditions. There thus results aconsiderable improvement in the quality of the finished gears.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be better understood and objects other than those setforth above will become apparent when consideration is given to thefollowing detailed description thereof. Such description makes referenceto the annexed drawings wherein throughout the various figures of thedrawings there have been generally used the same reference characters todenote the same or analogous components and wherein:

FIG. 1 shows the geometric relationships between a helical spur gear andthe associated reference or basic generating rack tooth flank in a firstgenerating position;

FIG. 2 shows the geometric relationship between a helical spur gear andthe associated reference or basic generating rack tooth flank in asecond generating position;

FIG. 3 shows the projection of the reference or basic generating racktooth flank on the transverse section plane in two generating positions,including the geometrical relationships of significant variables;

FIG. 4 shows the projection of the reference or basic generating racktooth flank on the transverse section plane and, superimposed thereupon,a rotation of the reference or basic generating rack tooth flank intothis transverse section plane, including the geometrical relationshipsof significant variables;

FIG. 5 shows a projection of the reference or basic generating racktooth flank according to FIG. 4, including significant geometricalvariables and relationships for two generating positions;

FIG. 6 shows the gear generating relationships between the gear toothflank and the machining tool surface in various generating positionsaccording to the state of the art;

FIG. 7 shows the gear generating relationships between the gear toothflank and the machining tool surface in various generating positionaccording to the invention;

FIG. 8 shows a variation of working or machining lines for processing oftooth flanks extending essentially along generatrices;

FIG. 9 shows a further variation of working or machining lines extendingessentially along helices or spiral lines;

FIGS. 10a, 10b and 10c show various grinding wheels suitable for theinventive method;

FIG. 11 shows simultaneously generated points of the second or innerdedendum portion of the tooth flank involute and the root fillet radiusor undercut;

FIG. 12 shows a depiction of the important motion axes of the inventivemethod when using a work or machining line comprising generatrixsegments wherein, for the sake of representational clarity, therelationships for fabrication of straight toothing are shown;

FIG. 13 shows a schematic diagram of a control device or means for anexemplary embodiment of a machine tool or gear generating machine;

FIG. 14 shows a schematic depiction of an exemplary embodiment of amachining tool or gear generating machine employing a working ormachining line having generatrix linear segments;

FIGS. 15a and 15b show the schematic depiction of a further exemplaryembodiment of a machining tool or gear generating machine employinghelical or spiral working or machining lines; and

FIG. 16 shows the two working or machining points of prior art methodswhen employing a generatrix working or machining line and using a dishedgrinding wheel.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Describing now the drawings, it is to be understood that to simplify theshowing thereof only enough of the apparatus for fabricating involutegear tooth flanks has been illustrated therein as is needed to enableone skilled in the art to readily understand the underlying principlesand concepts of this invention. In one exemplary embodiment of theinventive fabricating method for involute gar tooth flanks, theworkpiece or gear blank is in general horizontally or vertically clampedon a workpiece or gear table or rotary table equipped for performing therequisite generating feed motions. The tooth flank is subjected to agenerating roll motion in relation to machining surface of at least onegrinding wheel or disk and which machining surface corresponds to thetooth flank of the reference or basic generating rack profile. Thegrinding wheel or disk simultaneously performs a rotary slide orcarriage motion and a feed motion essentially along a generatrix of thetooth flank as a working or machining line. A traversing motion in thedirection towards the tooth flank (i.e. a feed motion) determines thedepth of cut. The workpiece or gear blank performs the generating feedmotion (generatrix envelope).

In addition to these feed motions, a supplementary feed motion isperformed which is tangential to the tooth flank, preferably tangentialas seen in transverse section (cf. FIG. 7). This supplementary feedmotion is a relative motion between the workpiece or gear blank and themachining tool or grinding wheel or wheels. The grinding wheel or diskis thus entrained together with its momentary or active and variablyselectable working or machining point in the direction of the gear toothflank and the prescribable or predeterminate and selectable working ormachining point moves on the tooth flank along a generatrix as aselectable or selectably predeterminate working or machining line, alsoknown as the operative line. The working or machining point on thegrinding wheel or disk remains (except for its rotation) at one pointand does not wander, as is the case with prior art methods, over theentire working or machining width of the grinding wheel or disk incorrespondence to the generating motions of the tooth flank on it. Theworking or machining point on the grinding wheel or disk is thusprescribable or predeterminate and selectable.

Furthermore, it is held in a prescribable working or machining region ofthe grinding zone independently of the grinding process. Consequently,this working or machining region can also be of smaller dimensions orextent than in prior art methods. This is especially advantageous withcoated tools, since the coating can then be applied to a smaller area.In particular, the supplementary feed motion can be controlled orgoverned in accordance with the formula or equation (FIG. 5):

    ys=h·tan γ+(w·sin αt)/cos γ(1)

wherein:

ys=distance of the working or machining point S from a contact point Mon the gear tooth flank;

w=generating path length; continuously

h=grinding stroke length; monitored

αt=pressure angle in transverse section; and

γ=angle between generatrix and pitch line of the generated tooth flank.

Turning now specifically to FIG. 5 of the drawings, a helical spur gearis seen in mesh with a hypothetical reference or basic generating rack.In the initial position of the generating roll motion and the grindingmotion, the contact line between the reference or basic generating racktooth flank and the gear tooth flank is the line Bo and a working areaor machining region meridian is the dotted line To. Consequently, theworking or machining point is the intersection point S of these twolines. As is depicted in FIGS. 3 and 5, the distance q between thecontact line Bo and a contact line B corresponds to the generating pathw and is related thereto according to the formula:

    q=w·sin αt                                  (2)

Consequently, during a generating path w and a grinding stroke h, theworking or machining point wanders towards S. The distance ys of point Sfrom an initial position M (chosen as reference point and advantageouslyas median point of the developed flank plane, i.e. of the generatingrack tooth flank) is calculated according to formulas given above. Thissupplementary feed motion, e.g. of the grinding wheel or disk, can besuperimposed on a work or machining point motion which discontinuouslyor continuously incrementally prescribably displaced the work ormachining point relative to its working area or machining region.Therefore, the working or machining point, for example during a givennumber of grinding wheel revolutions, can be held at a specific distancefrom the inside or the outside edge of the working or machining surfaceof the grinding wheel and subsequently brought into an adjacent positionfor the following revolution group (displacement cycle) until the wholeor a prescribable or predeterminate portion of the working area ormachining region of the machining tool, i.e. of the grinding wheel, hasbeen swept. Subsequently, a new displacement cycle of the grinding wheelis initiated. With this continuous prescribable or predeterminatedisplacement of the work or machining point, a spiral track or path isswept or traversed in the working area or machining region during eachdisplacement cycle. Nevertheless, it is not absolutely necessary thatthis work or machinig point displacement be performed in a cyclicalmanner. It is also possible to jump from one circular track or path toanother circular track or path.

The control of working or machining point displacement is performedaccording to prescribable or predeterminate conditions or values. Thesevalues or conditions are stored in any desired form on a data carrier,for example in the form of a curved guide template or as a cam guidedisk, in the form of a measuring point or pulse regulation by sensingthe machining tool or grinding wheel for signs of wear or itsoptimization or for better tool exploitation, or in the form of a pulsegenerator, an electronic data carrying medium, mass memory or the like.Especially the latter, either by themselves or in conjunction withmeasuring point regulation, can contain empirical values which have beenfound to produce optimal flank surface properties.

The traversing feed motion is carried out in a manner known per se whengrinding gear tooth flanks without topographical or geometriccorrections. If the case should arise that a tooth flank is to be groundwith a topographical or geometric correction, i.e. with a profile whichvaries over the width of the tooth, then either the correction motion issuperimposed on the feed motion or a correction motion issupplementarily, i.e. entailing more than one step, performed. This isessentially a question of control depending on which value is taken as areference value, respectively as an initial value, for the feed motion.It is necessary to fully traverse in each correction point from thisreference value in a single step or a number of steps. The assignment ofthe correction values to the individual points of the tooth flank isknown per se and is preferably done in a coordinate system of the fieldof action or machining engagement. Either the workpiece or gear blank orthe machining tool or grinding wheel can perform the traversing motion.

The working or machining line of the embodiment of the methodhereinbefore described can take the form of a zig-zag line whoseindividual segments each extend essentially along a generatrix of thetooth flank (cf. FIG. 8). In practice, however, the actual working ormachining line will always deviate somewhat from the theoretical workingor machining line. When using this working or machining line either theworkpiece or gear blank or, for very large workpieces or gear blanks,the tool or grinding wheel performs a continuous generating feed motion.In addition, the machining tool or tools are moved along the surface ofthe tooth flank with an oscillating or stroking feed motion. Anotherform is a meandering or wandering type of work or machining line inwhich the working or machining point is guided along a generatrix, or atleast approximately along a generatrix, as one branch of the segmentduring a stroke or stroking feed motion. For changing or switching overfrom one genertrix to a generationally relevant adjacent generatrix, theworking or machining point is guided along a profile line, possibly atooth or flank line as a second branch or segment of the working ormachining line. This depends on the position of the turning or reversingpoint relative to the tooth flank in the course of motion of thegrinding process. A discontinuous generating feed motion of theworkpiece or gear blank or a corresponding motion of the machining toolor tools results from this configuration of the working or machiningline when the machining tool or tools move about the stationaryworkpiece or gear blank. In this way the machining tool or tools performthe supplementary stroke or stroking feed motion.

In a further embodiment of the method for fabricating involute geartooth flanks, the workpiece or gear blank is, as usual, clamped to awork or machining table which performs generating feed motions. If thework table, in addition to the continuous generating feed motion, isalso rotated and either the work table or the machining tool or toolsare moved in accord therewith in the direction of the axis of the gear,then the working or machining point is displaced along a working ormachining line in the form of a helical or spiral zig-zag line on thetooth flank (tooth trace or flank envelope). The generating feed motion,the rotary motion and the axial feed motion are to be carried out suchthat they are mutually adapted to or match each other so that theworking or machining point always lies on the tooth flank. Therefore ahelical or sprial motion is superimposed onto a generating motion. Thegrinding wheel or disk carries out a supplementary feed motion whosedirection of motion lies in the working or machining plane or surface ofthe grinding wheel or disk, i.e. lies in a tangential plane of the toothflank, so that the selectable working or machining point or itsimmediate vicinity (the size of which depends on the form of thegrinding wheel) is essentially always guided along this working ormachining line.

The control of these motions can be the result of a combination ofelectro-mechanical control utilizing known means, for example forgenerating the generating feed motion, and of individual motor drivemeans, in which appropriate position sensors are connected to theregulating and control circuits. It is, however, also possible tocontrol these movements purely electronically with the reference valuesstored on the most various forms of data storage medium, for examplemechanical data storage media such as cam discs or template bars etcetera, magnetic data storage media, optical data storage media etcetera and, by means of the appropriate means for reading-out andtransmission and control, to transmit these values to the drive means.

Discontinuous control of the generating feed motion is also possible,although it can only be carried out in steps or increments. The workingor machining point is guided along a helical or spiral line of the toothflank and in the region of the flank end an incremental switch or changemovement is undertaken in the form of a generating feed motion whichpermits the subsequent generatrix envelope to occur. In this way, onegeneratrix envelope is juxtaposed with another generatrix envelope. Thegenerating feed motion can be performed either by the workpiece or gearblank o by the at least one machining tool or grinding wheel. Theworking or machining line then has a meandering course or path and itssegments consist of two branches: a tooth trace or flank line and aprofile line. Consequently, the profile line will, in general, lie onthe virtually extended tooth flank, i.e. outside the gear tooth flank.The supplementary generating feed motion of the machining tool must beperformed in accordance with the incremental feed motion, i.e. thegenerating motion, in order that the working point, despite theincrementation, be maintained in the same position relative to theworking or machining surface of the machining tool, i.e. the grindingwheel or disk.

If is is required that the working or machining point be continuously ordiscontinuously displaced within the working area or machining region ofthe machining tool in order to achieve a uniform wear of the machiningtool or to adapt the wear of the machining tool to the economica factorsof the machining operation, i.e. to optimize machining tool wear inrelation to the machining operation, then a further working or machiningpoint motion is performed. This can be superimposed on the supplementaryfeed motion or can be undertaken separately from it. The variablyselectable working or machining point, also called the operative point,is displaced relative to the machining tool on its working or machingsurface, i.e. on the effective cutting area or region of the grindingwheel. This can be achieved continuously according to a spiral line,discontinuously by circular lines or possibly via random number controlin order to achieve the most uniform and patternless wear possible ofthe grinding wheel or disk.

This further embodiment of the inventive method also allowstopographical or geometric correction traversing motions to be performedin addition to the normal traversing motion. These correction motionscan be controlled in a known manner from the field of action or ofmachining engagement and can be performed either purely rotationally ortranslationally by the workpiece or gear blank as well as by themachining tool or grinding wheel.

A further motion can be performed in each of the embodiment of themethod, namely the generally noncontinuous adjustment of the toolsupport by a variation amount of the helix angle β of helical teeth.This adjustment makes possible, especially when employing dishedgrinding wheels or disks of conventional construction, a substantialreduction of the circumference of the working or machining point toalmost exactly a point. This motion, just as the other motions, can alsobe performed by a control program. Here, too, the program can be storedon mechanical or magnetic storage media and can be brought into serviceby means of appropriate data transmission means, for instancemechanical, optical, electrical or magnetic means.

Depending on the working line, a different generatrix envelope networkresults from each of these embodiments of the method. This generatrixenvelope profile network can be optimally configured by means of anappropriate adjustment or matching of the feed and traversing motionswith respect to the corresponding variables.

If method with helical or spiral working lines are employed, or ifmethods with helical or spiral lines which consist of various componentsegments are employed, then there results the important advantage thatthe tool support or head of the machine tool or gear cutting machine ismoved not along an inclined straight line but rather along a vertical.Consequently, the machine is not loaded by the displacement of theweight of the tool head, a load which may be quite considerabledepending on the operating speed. This contributes substantially to thefabrication accuracy of the workpieces or gears.

It represents an important advantage if the correction traversing motioncan be performed by the machining tool, since workpiece or gear blankmotion is then saved. In this way the stability of the machine can besubstantially increased and vibrations can be avoided.

Depending on the application, in the embodiment of the method withhelical or spiral component segments for the machining line, thegeneratrix envelope can be controllably concentrically orquasi-concentrically altered, on the one hand, and controlled in width,on the other hand. In particular, the generatrix envelope widths in theregion of the tooth head or addendum and the tooth root or dedendum canbe carried out in different widths.

If only simple dedendum or addendum corrections are to be performed,then they can be generated when employing the tooth trace or flank lineenvelopes by means of simple relative motions. In principle, thecalculation and execution of flank corrections is simpler in this case,since the envelopes of tooth trace or flank lines are limited. Forexample, the same values are used during a complete grinding stroke innormal profile corrections. With the choice of appropriate values forthe correction parameters, profile corrections can also be generated bytangential motions. It is also basically possible to make use ofcorrected tools, for example grinding wheels or disks or milling face orside cutters. Slot milling cutters or end mills or the like can also beused. Analogously, the same values are always set for each envelope whenperforming longitudinal corrections.

In each of the described exemplarily embodiments of the inventivemethod, that is with a generatrix machining line and with helical orspiral component segments in the working or machining line, it isadvantageous that topographical or geometric corrections can beperformed much more accurately than heretofore, since they are generatedusing practically a single working or machining point and the desiredcorrection values are freely prescribable. Furthermore, grinding wheelswith flat or conical working or machining surfaces can be used. Theseworking or machining surfaces are easily produced and maintained.

The choice between both variations of the method will be made accordingto the individual application. If, for example, it is required that onlyvery small or almost no profile differences should occur between thetooth ends and the tooth center and it is necessary to work with acontinuous generating feed motion, then the method described as thesecond examplary embodiment and having helical or spiral lines assegments or components of the working or machining line will beparticularly advantageous.

Neither of the two embodiments of the method require tools which arespecific to the workpiece or gear blank and none of them require toolcorrection devices with the associated maintenance and inspection work.

FIG. 14 depicts an exemplary embodiment of a machine tool or gearcutting machine for performing the method of the invention forfabricating a gear wheel 1.0 using generatrices as the working ormachining line. There is provided, as usual, a machine frame 1.1 whichon one side carries a displaceable or translatable generating motioncarriage or slide 1.2 and on the other side a cross or transverse slideor carriage arrangement 1.3 of a type known per se and which isswivellably mounted for adjusting the tooth helix angle. A tool support1.4, on which a machining tool or tools, for example grinding wheels ordisks 1.5, are seated or fastened, is fixed to the cross or transverseslide or carriage arrangement 1.3. A correspondingly adjustable feedslide or carriage 1.6 is provided for carrying out the supplementaryfeed motion with which the working or machining point of each of thegrinding wheels or disks 1.5 is guided tangentially to the gear toothflank to be fabricated. Preferably, motion or displacement transducersor other position indicators or sensors 1.7 are provided on all of theslides or carriages. These position indicators or sensors 1.7 areconnected with a control arrangement 2.0 (shown in FIG. 13). Thiscontrol arrangement 2.0 can be either purely electronic or amechanically and electronically operated control means. For example, thegenerating motion can be derived in conventional manner from agenerating tape control means. The drive motors also possess rotaryspeed transducers 2.2 (FIG. 13) which are connected with the controlarrangement 2.0. For the sake of expository simplicity, it will beassumed that the machine tool shown in FIG. 14 contains anelectromechanical control means in which the generating tape controlmeans is of a type known per se and therefore not shown in FIG. 14 andalso not described in detail here.

Such a control means (cf. FIG. 13) possesses a master computer orcontrol processor 2.3 which contains and runs the basic control program.It is connected with a master control interface 2.4 for controlling andmonitoring each tool support 1.4 as well as the other not particularlymentioned motions such as, for instance, the stroke or stroking feedmotions, the adjustment motion of the tooth helix angle β and itsdeviations from the reference value, positional motion of the workpieceor gear blank as well as other necessary and known movements. Thismaster control interface 2.4 is connected to each of the followingcontrol and monitoring devices:

a grinding wheel control means 2.5 for the grinding wheel or disk;

a carriage control means 2.6 for controlling pressure angle, tooth helixangle and intermediate slide motion;

a supplementary feed control means 2.7 for the supplementary feedmotion;

a traversing control means 2.8 for the traversing motion as well as thenormal cutting or grinding, i.e. machining motion and also the normaland topographical or geometric correction motions; and

a wear control means 2.9 for the grinding wheel measuring device formeasuring grinding wheel wear and for performing diameter compensationet cetera.

A regulator 2.51 is connected to the grinding wheel control means 2.5and also to a grinding wheel drive means 3.1. A rotary speed transducermeasuring means or system or tachometer 2.2 is connected to the grindingwheel drive means 3.1 and is also connected to the grinding wheelcontrol means 2.5. This feedback regulation circuit serves for accuraterevolution or speed regulation in cooperation with the other controlledmotions and machine functions.

The carriage control means 2.6 for intermediate slide or carriagemotion, pressure angle and helix angle is connected to a monitoringarrangement 2.62 for position feedback and a second regulator 2.61 whichis connected on one side to an intermediate slide or carriage drivemeans 3.2 for positioning each of a first or right hand control axis Urand a second or left hand control axis U1 of the machine tool or gearcutting machine illustrated in FIG. 12 and on the other side with adrive means 3.3 for adjusting the pressure angle α or the tooth helixangle λ or both. The intermediate slide or carriage drive means 3.2 isconnected to a position indicator or sensor 2.63 which in turn isconnected with the carriage control means 2.6 for controlling pressureangle, helix angle and intermediate slide or carriage motion. The drivemeans 3.3 for adjusting the pressure angle α or the tooth helix angle βor both is also connected to a position indicator or measuring system2.64 (which is not shown in FIG. 8 due to the conical grinding wheelsemployed), whose measuring data is transmitted to the carriage controlmeans 2.6 for controlling pressure angle, helix angle and intermediateslide or carriage motion. The reference data for each position aretransmitted to this carriage control means 2.6 by the master controlinterface 2.4 and the carriage control means 2.6 returns its own databack to the master control interface 2.4.

The supplementary feed control means 2.7 for the supplementary feedmotion is also connected through its input and output means to themaster control interface 2.4 and is connected through an input means toa monitoring interface 2.72 for monitoring the positions of thecontrolled components. The supplementary feed control means 2.7 is alsoconnected to a third regulator 2.71 which controls the drive means 3.4for the supplementary feed motion. A position measuring system orindicator 2.73 is connected to this drive means 3.4. The positionmeasuring system 2.73 feeds its measuring data for the supplementaryfeed motion to the supplementary feed control means 2.7.

A monitoring means 2.82 for the end or reversing positions and theworking or machining positions of the guide means is connected to thetraversing control means 2.8 for the normal and the topographical orgeometric corrections of the tooth flanks. A fourth regulator 2.81 forthe drive means 3.5 of the traversing and correction motions of themachining tool or each machining tool 1.5 is connected to the traversingcontrolm eans 2.8. This drive means 3.5 can also cooperate with amachine axis which is associated with a workpiece or gear blank so thatthe traversing motion is performed by the workpiece or gear blank 1.0. Aposition measuring system or indicator 2.83 is connected to this drivemeans 3.5 and transmits its signals to the traversing control means 2.8for the traversing and correction motions.

The wear measuring control means 2.9 is for controlling, monitoring andprocessing measurement data and is connected to measurement and positionindicator means as well as monitoring means and drive output means. Itcommunicates with the master computer or control processor 2.3 throughthe master control interface 2.4.

All these control means 2.5 to 2.9 communicate with the master controlinterface 2.4 and the master control interface 2.4 exchanges signals ordata with the master computer or control processor 2.3 so that allmotions are interrelated and controlled in accordance with theregulating and measuring data.

In FIG. 12 only the most important axes to be controlled are shown.These are:

WL, WR=two, i.e. left and right hand, branches or segments of thegenerating motion;

rfs=positional axis between machining tool or tools and workpiece orgear blank;

UTL', UTR=left and right hand traversing axes for machining traverse andcorrection traverse;

OL', OR=left and right hand axes of the supplementary feed motions;

αSL', αSR=left and right hand pressure angle adjustment axes;

UL', UR=left and right hand intermediate slide or carriage axes;

βS', SβS=tooth helix angle and its variations;

h=machining tool or grinding wheel stroke.

Grinding wheels or disks are preferably utilized as the machining orgrinding tools 1.5. These can have the well-known basic form which issubstantially that of a dish or disk or that of a double cone, as isshown in FIGS. 10a and 10b. In consequence of the supplementary feedmotion utilized according to the method of the invention, the workingareas or machining regions of the grinding wheels or disk can be keptsubstantially narrower than in heretofore known grinding methods. Aparticularly advantageous form of grinding wheel or disk is shown inFIG. 10c. This type of grinding wheel is a modified dished wheel or diskand possesses instead of a planar working or machining surface a conicalfrustum having an included or cone angle slightly less than 180°. Thisform of grinding wheel or disk unites the advantages of the dished wheelwith those of the conical wheel.

An exemplary apparatus for carrying out the grinding method of theinvention employing a working or machining line with helical or spiralcomponent segments can be very similar to the apparatus hereinbeforedescribed. This apparatus also comprises a machine frame 1.1 which onone side carries a displaceable generating carriage or slide arrangementand on the other side a pivotably mounted cross or transverse slide orcarriage arrangement 1.3 known per se for adjusting the helix angle.However, for the helical or spiral working or machining line, at leastone component or portion of the slide or carriage complex must beguidable parallel to the axis of the machining tool in a stroke feedmotion. For this purpose, a further slide 1.10 in accordance with FIG.15b or an addition swivel axis 1.11 in accordance with FIG. 15a must beprovided between the machine frame 1.1 and one slide or carriage.Alternatively, the motions are so controlled that the resultant motionis identical with this stroke feed motion. The difference liesessentially in the temporal control of the individual motions forachieving the tooth flank form.

The control of these motions can be most readily realized by means of anarrangement of individual drives or drive means for each motion. Thetooth helix is in this case achieved not through a stroke motion of astroke slide or carriage or a corresponding slide or carriagearrangement performed at an inclination towards the gear axis, but bymeans of a slide or carriage which is displaceable parallel to the gearaxis.

In order to employ the helix or spiral as a component segment of theworking or machining line, the workpiece is rotated on the workpiececarrier or support. Only at the end of the tooth trace or flank line isthe incrementation performed for generating the next envelope of theworkpiece or gear blank by means of the generating drive means utilizingeither an electronically controlled drive means or a conventionalgenerating tape control means.

For carrying out the normal or the topographical or geometriccorrections, control means are provided which cooperate with the drivemeans for the individual motion axes. The operating sequence of themotions is determined by mechanical, magnetic, optical or electricalstorage media. The motions can be carried out such that the correctiontraverses of the machining tool are purely rotary, purely translatory ora combination of the two. To achieve this, the drive mean are activatedso that the desired resultant motions arise. The supplementary rotationor angular displacement of the gear or rotary table, i.e. the work ormaching table, amounts to:

    nt=Fk/db                                                   (3)

wherein:

Fk=Flank correction value

db=Base circle diameter

nt=Supplementary motion of the gear or rotary table

The control means for generatrix envelope optimization is also similarlystored on storage media as a sequence of signal sequences cooperatingwith position indicators and can be fed into the control means for theindividual motion sequences. The required freedom of play in the drivecan only be achieved with great difficulty or with great design outlaywhen employing prior art drives. For instance, a double-worm drive wouldbe necessary for the gear or rotary table. With the inventive individualdrive arrangement controlled by command sequence, this play can beachieved very easily.

While there are shown and described present preferred embodiments of theinvention, it is to be distinctly understood that the invention is notlimited thereto, but may be otherwise variously embodied and practicedwithin the scope of the following claims.

Accordingly, what I claim is:
 1. A method of fabricating involute geartooth flanks both with and without geometric correction on a machinehaving at least one machining tool and in which method machiningmotions, feed motions and traversing motions between the machining tooland a gear blank are performed, comprising the steps of:confiningmachining contact between said at least one machining tool and said gearblank at least to the immediate vicinity of a selectable machining pointon said machining tool; performing said feed motions such that saidmachining point is guided substantially along a selectablepredeterminate machining line lying at least approximately on a toothflank surface of a gear tooth of a gear being fabricated from said gearblank for generating a gear generatrix envelope; said step of confiningmachining contact entails confining said selectable machining pointwithin a predeterminate machining region of said at least one machiningtool during machining by means of a supplementary feed motion of said atleast one machining tool; said selectable machining point of said atleast one machining tool is continuously displaced within saidpredeterminate machining region during machining by a controllablemachining point motion related to machining tool wear; and saidcontrollable machining point machine being superimposed upon saidsupplementary feed motion of said at least one machining tool and asupplementary feed motion of said gear blank towards said at least onemachining tool.
 2. The method as defined in claim 1, wherein:saidcontrollable machining point motion is continuously superimposed uponsaid supplementary feed motion of said at least one machining tool andsaid supplementary feed motion of said gear blank towards said at leastone machining tool.
 3. The method as defined in claim 1, wherein:saidcontrollable machining point motion is discontinuously superimposed uponsaid supplementary feed motion of said at least one machining tool andsaid supplementary feed motion of said gear blank towards said at leastone machining tool.
 4. A method of fabricating involute gear toothflanks both with and without geometric correction on a machine having atleast one machining tool and in which method machining motions, feedmotions and traversing motions between the machining tool and a gearblank are performed, comprising the steps of:confining machining contactbetween said at least one machining tool and said gear blank at last tothe immediate vicinity of a selectable machining point on said machiningtool; performing said feed motions such that said machining point isguided substantially along a selectably predeterminate machining linelying at least approximately on a tooth flank surface of a gear tooth ofa gear being fabricated from said gear blank for generating a geargeneratrix envelope; said step of confining machining contact entailsconfining said selectable machining point within a predeterminatemachining region of said at least one machining tool during machining bymeans of a supplementary feed motion of said at least one machiningtool; continuously measuring first values of a generating path of acenter point of said gear blank; continuously measuring second values ofa grinding wheel stroke or longitudinal feed in relation to apredetermined reference point; and controlling said supplementary feedmotion of said at least one machining tool by means of said first valuesand said second values such that the equation:

    ys=h·tan γ+(w·sin α)/cos γ

is at least approximately satisfied; wherein: ys is a distance of saidselectably predeterminate machining point common to said at least onemachining tool and said gear blank from said predetermined referencepoint; w is a generating path length; γ is an angle between saidgeneratrices and a pitch line of the tooth flank; h is a grinding strokelength; and αt is a pressure angle measured in transverse section.
 5. Amethod of fabricating involute gear tooth flanks both with and withoutgeometric correction on a machine having at least one machining tool andin which method machining motions, feed motions and traversing motionsbetween the machining tool and a gear blank are performed, comprisingthe steps of:confining machining contact between said at least onemachining tool and said gear blank at least to the immediate vicinity ofa selectable machining point on said machining tool; performing saidfeed motions such that said machining point is guided substantiallyalong a selectably predeterminate machining line lying at leastapproximately on a tooth flank surface of a gear tooth of a gear beingfabricated from said gear blank for generating a gear generatrixenvelope; and said step of confining machining contact entailingconfining said selectable machining point within a predeterminatemachining region of said at least one machining tool during machining bymeans of a supplementary feed motion of said machining tool and asupplementary feed motion of said gear blank toward said machining tool.6. The method as defined in claim 5, wherein:said gear being fabricateddefines tooth spaces; each tooth space of said tooth spaces having asymmetry plane; and said supplementary feed motion of said machiningtool being performed along said symmetry plane.
 7. The method as definedin claim 5, wherein:said supplementary feed motion of said gear blanktoward said machining tool is a translatory motion.
 8. The method asdefined in claim 5, wherein:said supplementary feed motion of said gearblank towards said machining tool is a rotary motion.
 9. The method asdefined in claim 5, wherein:said supplementary feed motion of said gearblank towards said machining tool is a pure generating feed motion. 10.The method as defined in claim 5, wherein:said involute gear toothflanks have a generatrices; said generatrices defining generatrixenvelopes of said involute gear tooth flanks; and said supplementaryfeed motion of said machining tool and said supplementary feed motion ofsaid gear blank towards machining tool being coupled with said feedmotions performed between said machining tool and said gear blank alongsaid selectively predeterminate machining line for fabricating involutegear tooth flanks according to said generatrix envelopes.
 11. The methodas claimed in claim 10, wherein:said selectively predeterminatemachining line comprises component segments; and said component segmentsat least approximating said generatrices.
 12. The method as defined inclaim 10, wherein:said involute gear tooth flanks have profile lines;said selectively predeterminate machining line comprising componentsegments; at least one component segment of said component segmentscomprising a first branch; at least one component segment of saidcomponent segments comprising a second branch; said first branch atleast approximating one of said generatrices; and said second branch atleast approximating one of said profile lines.
 13. The method as definedin claim 5, wherein:said involute gear tooth flanks have tooth traces;said tooth traces defining tooth trace envelopes of said involute geartooth flanks; and said supplementary feed motion of said machining tooland said supplementary feed motion of said gear blank towards saidmachining tool being coupled with said feed motions performed betweensaid machining tool and said gear blank along said selectivelypredeterminate machining line for fabricating involute gear tooth flanksaccording to said tooth trace envelopes.
 14. The method as defined inclaim 13, wherein:said selectively predeterminate machining linecomprises component segments; and said component segments at leastapproximating said tooth traces.
 15. The method as defined in claim 13,wherein:said involute gear tooth flanks have profile lines; saidselectively predeterminate machining line comprising component segments;at least one component segment of said component segments comprising afirst branch; at leastone component segment of said component segmentscomprising a second branch; said first branch at least approximating oneof said tooth traces; and said second branch at least approximating oneof said profile lines.